The present invention relates to an exhaust gas treatment device.
For the treatment, more particularly for the purification, of exhaust gases of internal combustion engines, e.g., diesel engines of passenger automobiles, it is known to arrange porous, gas permeable substrates in a closed housing in an exhaust pipe, so that the exhaust gas flows through the substrate.
To this end, it is known to bring the substrate into the shape of a hollow body having one or more walls, the hollow body being arranged in the housing such that the exhaust gas must always flow through at least one wall of the hollow body in order to pass from the entrance of the housing to the exit thereof.
Possible geometries to be used for the hollow body include, e.g., a pair of truncated cones fitted inversely into each other or a pair of cylinders arranged concentrically in relation to each other.
To form the substrate for the hollow body, plates made from a metal foam, a metal sponge or else a metallic hollow sphere structure are used, for example, which may be coated with a catalytically active material. An exhaust gas treatment may be effected, e.g., by chemical conversion, mechanical deposition of particles, e.g., soot particles, carried along with the exhaust gas, in the pores of the substrate, or by a combination of different methods.
The hollow body, in particular a hollow body made from metal foam plates, and the housing, which in most cases consists of sheet metal, have, however, different coefficients of thermal expansion, which become noticeable with exhaust gas temperatures that may amount to several hundred degrees Celsius. An additional complication is that the substrate is relatively brittle and is therefore highly stressed by different linear expansions of the hollow body and of the housing.
It is the object of the invention to present an approach that takes the different dimensions of the hollow body and of the housing into account in a simple way.